I haven't had a need for this feature so far, therefore I had to do a bit of RTFM followed by some "poking around". But in the end its pretty simple: Apart from having the virtualbox-ose-additions.tcz extension installed one also needs to ensure that the "active component on the inside" is running. I therefore started it via sudo VBoxService, and following this 'VBoxManage guestcontrol' worked for me.

Some further remarks:

to be able to "see" the 'stdout' output the '--wait-stdout' option has to be added to the 'VBoxManage guestcontrol' command,

to be able to "see" the 'stderr' output the '--wait-stderr' option has to be added to the 'VBoxManage guestcontrol' command; doing this OTOH prevented me to "see" the 'stdout' output and even adding '--wait-stdout' as well did not change the outcome,

any arguments for the remote command execution need to be added at the end of the 'VBoxManage guestcontrol' command (preceded by '--').

So all together: if one wants to run 'ls -lRa /home/tc/.local' (in a VM called 'TC4') this could be done like this: